The field of the invention comprises electrical plugs and sockets for interconnecting electric cables and extension cords. In particular, applicant's invention is directed to plugs and sockets that can be conveniently attached and detached without tools but cannot be detached by pulling on the extension cords or cables.
Common extension cords and cables for household and office use at 110 volts and 15 amperes AC utilize simple two or three prong plugs and sockets. The plugs and sockets are attached and detached axially by pushing together or pulling apart respectively. The plugs and sockets can easily be detached inadvertently with a sudden pull, in particular when being dragged about and around obstacles.
Common 220 volt AC extension cord plugs and sockets are typically of a larger size and incorporate bayonet or other latching means on at least one prong of the plug engageable with a twist relative to the socket to prevent inadvertent disengagement. Such extension cords are frequently used in construction projects for portable electric hand tools. With eventual wear the latching means fails and the extension cords become easily detached as they are dragged about obstacles.
As a result over the years more sophisticated means to latch plugs and sockets together have been developed. U.S. Pat. No. 904,603 illustrates a cable connector for a single wire wherein the plug and socket are identical and external rotatable sleeves having camming means attach the plug and socket together. U.S. Pat. No. 1,835,251 discloses a substantially conventional plug and socket with external latches to positively retain the plug and socket together. French Pat. No. 811,155 discloses a bulbous identical plug and socket for dual wires wherein the units are pushed together and twisted to positively engage the electrical contacts and retain the units together.
U.S. Pat. No. 2,506,979 discloses identical plug and socket connectors that telescope together and latch with a slight twist and U.S. Pat. No. 3,252,124 discloses a push in and twist identical connector pair for multiple pole or wire connection. In general the prior art plug and socket connectors rely upon the prongs or external devices to positively retain the connectors together, the connectors otherwise being easily detachable with a simple pull.